1. Field of the Invention
This invention relates to an attenuating element which utilizes a yttrium-iron-garnet (YIG) material, and more particularly to a method of fabricating a plurality of such elements at one time.
2. Description of the Related Art
Frequency selective limiters (FSL) are attenuating devices which utilize a yttrium-iron-garnet (YIG) material having the property of being able to attenuate higher power level signals while simultaneously allowing lower power level signals separated by only a small frequency offset from the higher level signals to pass with relatively low loss. YIG-based FSL's are capable of limiting or attenuating across more than an octave bandwidth in the 2-8 GHz range. Higher power level (above-threshold) signals within the device bandwidth will be attenuated without requiring tuning of the FSL. Lower power level (below-threshold) signals separated from the higher power level signals by more than a few spin wave line widths will pass through the FSL without experiencing any greater loss than if the higher power level signals were not present. For an attenuating device based on YIG, this selectivity bandwidth is on the order of between 20-50 MHz.
A portion of a fully assembled FSL 10 is illustrated in perspective in FIG. 1. Signal carrying conductor 12 is positioned between first and second YIG layers or slabs 14, 16. Both first and second YIG slabs 14 and 16 have a generally planar configuration, and the second YIG slab 16 has an overall length less than the overall length of the first YIG slab 14. As a result, the end portion 18 (one shown) of the signal carrying conductor 12 extends outwardly beyond the transverse edge 20 (one shown) of second YIG slab 16. The YIG slabs 14 and 16 and the signal carrying conductor 12 are supported on a metallized substrate 22 and are surrounded by a ground plane 24. Jumpers (not shown) may be utilized to serially connect a plurality of FSL's 10. The thickness of each YIG slab 14 and 16 may be varied to make the impedance of the signal carrying conductor 12 compatible with amplifiers and other external circuits (not shown). It has been found that increasing the thickness of the YIG slabs 14 and 16 increases the level of attenuation per unit length of YIG material at a given power level above some threshold power level. The apparatus shown in FIG. 1 is described in greater detail in a copending U.S. patent application entitled "Frequency Selective Limiting Device", Ser. No. 07/169,926, filed Mar. 18, 1988, now U.S. Pat. No. 4,845,439, in the name of Steven N. Stitzer et al. and assigned to Westinghouse Electric Corporation the assignee herein.
The processing technique used thus far for making individual FSL units 10 has consisted of cutting all of the parts of the structure to final size from standard wafers, then processing the individual parts through a series of steps. Individual parts processing is labor intensive and uniformity in the final product is difficult to achieve on a regular basis. In addition, the expense involved in individual parts processing can be considerable.